JPH0244005Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention automatically slightly opens the exhaust valve or intake valve when starting a general-purpose four-stroke engine, reduces the mixture compression pressure in the combustion chamber, This invention relates to an improvement of a pressure reducing device for reducing the starting force at the time of starting and improving startability.

(Prior art and its problems) In general, when starting a general-purpose 4-stroke engine, especially when starting a large engine by hand with a recoil starter, it requires a very large amount of effort, and the starting force at the time of starting is very low. Recently, there has been an increasing demand for reducing the amount of energy generated by the engine, and as a countermeasure, the exhaust valve or intake valve is automatically slightly opened when the engine is started, reducing the mixture compression pressure in the combustion chamber and increasing the starting force at the time of starting. An automatic pressure reducing device has been developed and put into practical use that reduces the pressure, increases the rotational speed after startup, and automatically releases the effect when the set rotational speed is reached.

A typical example of this type of automatic pressure reducing device will be explained with reference to FIG. 7. As the camshaft 1 rotates, the cam 2 provided on the camshaft 1 reciprocates the tappet 3 to open and close the intake and exhaust valves 5 of the combustion chamber 4. In a four-cycle engine, an arc-shaped movable member 7 is attached to a pin 8 on one half of the side surface of a gear 6 that is integrated with a camshaft 1 that has a cam 2 that operates one of the valves 5. An arc-shaped movable member 10 is attached to the other half of the side surface of the gear 6. A guide 12 consisting of a plurality of semicircular recesses is provided on the outer peripheral edge of the other end of the movable member 10, and one end thereof is supported by a pin 11 at one end of the movable member 7.
2 to the pin 13 attached to the side of the gear 6,
A spring 14 is stretched between the other end of the movable member 10 and the movable member 7.
In this automatic pressure reducing device, the other end of the movable member 7 is attracted by the spring 14 during low-speed rotation when the engine is started, so that each movable member 7, 10
is held in a predetermined position, and the arm 9 extending laterally from the inner peripheral edge of the movable member 7 protrudes outward from the cam base circle 2a, so that the tappet 3 is moved in the compression stroke every time the camshaft 1 rotates once. Push up and open valve 5.
is slightly opened to release the compressed air-fuel mixture and reduce the pressure, reducing the starting force at the time of starting, and when the rotational speed of the engine increases, the movable members 7 and 10 resist the spring 14 due to centrifugal force and move the pins 8 and 13. Since the arm 9 rotates outward as a fulcrum, the arm 9 is attached to the base circle 2a of the cam 2.
Located further inward, the pushing up action of the tappet 3 is eliminated, the valve 5 remains completely closed during the compression stroke, and the valve 5 is opened and closed normally by the cam 2 on the camshaft 1.

However, since such an automatic pressure reducing device has two movable members operated by centrifugal force, precision is required in component dimensions and assembly, and the structure is complicated and costs are high. In addition, since there are two movable members, the frictional resistance and the viscous resistance of the oil between the movable member and the pin portion and gear side surface that slide on the movable member will vary greatly, and the set rotational speed at which the decompression effect is canceled will increase. The problem was that it was not stable.

(Purpose of the invention) The present invention was made to eliminate these drawbacks, and has a simple structure, stable function, and easy assembly.Moreover, there is only one movable member that acts centrifugally when the camshaft rotates. The purpose of this invention is to provide an automatic pressure reduction device for a four-cycle engine that does not necessarily require the attachment of a spring that attracts the movable member, and that operates reliably.

(Structure of the invention) The automatic pressure reducing device for a general-purpose four-stroke engine of the invention has the following features: 1. The rotation of the camshaft causes the cam on the camshaft to reciprocate the tappet, thereby reducing the suction and air pressure in the combustion chamber.
It is applied to 4-cycle engines that open and close exhaust valves.

2. A movable member is placed on the side of a gear that is integrated with a camshaft that has a cam that operates one of the intake and exhaust valves of the combustion chamber so as to surround the camshaft, and the movable member is established 2
It is engaged with the gear so as to slide in a regulated direction by two guide grooves and two pins provided on the side of the gear.

3. A tappet push-up arm is protruded from the movable member to push up the tappet during the compression stroke of the engine.

4. During cranking when starting the engine, the centrifugal force acting on the movable member is caused by the force of gravity opposing the centrifugal force, the frictional force between the guide groove and the pin, and the action of the return spring tensioned between the gear and the movable member. At least one of the guide grooves and the pin receive the return force of the movable member that is applied to the tappet push-up arm by the valve spring so that the force does not exceed the cam base circle. It is arranged so that it is held outside.

5. During normal rotation of the engine, the centrifugal force acting on the movable member exceeds the gravity opposing the centrifugal force, the frictional force, and the acting force of the return spring, so that the movable member is moved along the guide groove. The tappet push-up arm is positioned at the same position as the cam base circle or inside the cam base circle.

(Embodiment) An embodiment of an automatic pressure reducing device for a four-stroke engine according to the present invention will be described with reference to FIGS. 1 and 2. 1 is a camshaft, 2 is a cam provided on the camshaft 1, and 3 is a tappet that opens and closes an intake valve or an exhaust valve 5 of a combustion chamber 4, and is reciprocated by the rotation of the cam 2. Reference numeral 6 denotes a gear fixed on the camshaft 1 adjacent to the cam 2. A movable member 20 is disposed on the side of the gear 6 so as to surround the camshaft 1. The outer side of the gear 6 is supported by pins 23 and 24 attached to the sides of the gear 6 through an oblong guide groove 21 and an L-shaped guide groove 22 provided diagonally at both ends facing each other with the center as the center. It is made to be able to slide in the direction. A tappet push-up arm 25 is extended from the movable member 20 to push up the tappet 3 at least during the compression stroke of the engine. In this example, between the tappet push-up arm 25 and a hole 26 drilled in the side surface of the gear 6, the tappet push-up arm 25 is moved outward from the base circle 2a of the cam 2 during cranking when starting the engine. A spring 27 is provided to force the protrusion. Further, the base circle 2a of the cam 2 is partially cut out because the tappet push-up arm 25 is extended.

Next, another embodiment of the automatic pressure reducing device for a four-stroke engine according to the present invention will be described with reference to FIG.
Since the same reference numerals in the figure as in FIG. 1 indicate the same members, the explanation thereof will be omitted. The movable member 28 has a substantially heart-shaped through hole 29 bored in the center, and is fitted to the side of the gear 6 so as to surround the camshaft 1 in the through hole 29. A tappet push-up arm 25 that pushes up the tappet 3 during the compression stroke of the engine extends toward the cam 2 from the recessed portion 29a. The movable member 28 has L-shaped guide grooves 3 provided on both left and right sides of the camshaft 1 in a direction perpendicular to the reciprocating direction of the tappet 3.
It is supported by pins 32 and 33 attached to the side surface of the gear 6 through a guide groove 31 having an L-shaped notch and is slidable toward the outside of the gear 6.

(Function) The automatic pressure reducing device of the embodiment shown in FIGS. 1 and 2 configured as described above has a movable member 2
is attracted by the spring 27, and the gear 6
The pins 23, 24 and the guide groove 21 attached to the
22 and is in a predetermined position having a pressure reducing function.

Movable member 2 during cranking when starting the engine
0 receives a centrifugal force corresponding to the rotational speed of the camshaft 1, but gravity and pin 24 counteract the centrifugal force.
Since the combined force of the frictional force between the guide groove 22 and the acting force of the spring 27 does not exceed the centrifugal force, the movable member 20 does not move relative to the gear 6, and the tappet push-up arm 25 moves toward the cam. It protrudes outward from the base circle 2a of No. 2. Therefore, during the compression stroke, the tappet 3 moves into the guide groove 22 via the push-up arm 25.
and is pushed up while being supported by the pin 24, and before the top dead center
The valve 5 is opened to approximately 40 degrees, and the compressed air-fuel mixture escapes and is depressurized, reducing the starting force at the time of starting.

When the rotational speed of the engine gradually increases and enters a normal operating state, the movable member 20 is pinned by centrifugal force against the combined force of gravity, frictional force, and the acting force of the spring 27, which opposes the centrifugal force. 23, the pin 24 on the opposite side hits the bent part of the guide groove 22, and from there the pin 24 rotates around the guide groove 22.
Since the guide grooves 21 and 21 face in the same direction, the movable member 20 slides toward the outside of the gear 6 as shown in FIG. When the valve 5 is retracted into the camshaft 1, the pushing up action of the tappet 3 is eliminated, and the valve 5 remains completely closed during the compression stroke.

When the engine is stopped, the centrifugal force caused by the rotation of the camshaft 1 disappears, so the movable member 20 is attracted by the spring 27 and returns to a predetermined position having a pressure reducing function as shown in FIGS. 1 and 2.

In this embodiment, the movable member 20 is connected to the spring 2.
7, the main purpose of the spring 27 is to force the movable member 20 to a predetermined position with a pressure reducing function when the engine is stopped. In the case of a general vertical engine, the gear 6 rotates counterclockwise when viewed from the front in Figure 1 even without the spring 27, and the guide grooves 21 and 22 rotate in the direction from the upper right to the lower left when viewed from the front in Figure 1. Because the tappet 3 is perforated, when the centrifugal force becomes small, such as immediately before the engine stops, if the tappet rotates at least once, the pressure reduction function will be activated just before the tappet 3 is pushed up, as shown in the rotational movements in Figures 6a to 6e. Return to the predetermined position with . Arrow G in FIG. 6a indicates the direction of gravity, and arrow T indicates the direction of rotation of the cam gear.

In the automatic pressure reducing device of another embodiment shown in FIG. 4, when the engine is stopped, the movable member 28 is in a predetermined position having a pressure reducing function by means of pins 32, 33 attached to the gear 6 and guide grooves 30, 31.

During the very low speed rotation at the beginning of engine startup, the movable member 2
8 receives a centrifugal force corresponding to the rotational speed of the camshaft 1, and the guide groove 3 opposes the centrifugal force.
0 and the pin 32 and the friction force between the guide groove 31 and the pin 33, the movable member 28 does not move in position relative to the cam gear 6, so the tappet is not pushed. The raising arm 25 protrudes outside the base circle 2a of the cam 2, and during the compression stroke, the tapepet 3 is pushed up while being supported by the guide groove 30 and pin 32 and the guide groove 31 and pin 33 via the push-up arm 25. , the valve 5 is opened to approximately 40 degrees before top dead center, the compressed air-fuel mixture escapes and is depressurized, and the starting load is reduced.

When the rotational speed of the engine gradually increases and enters the normal operating state, the movable member 28 is affected by the centrifugal force acting on the movable member 28 as shown in FIG. In order to exceed the frictional force of the pin 32,
33 toward the outside of the gear 6 in a direction oblique to the reciprocating direction of the tappet 3, the tappet push-up arm 25 retracts into the notch inside the base circle 2a of the cam 2, and the tappet 3 is no longer pushed up, and valve 5 remains completely closed during the compression stroke.
The valve 5 is normally opened and closed by a cam 2 on a camshaft 1.

This example was carried out on a vertical engine in which the axis of the camshaft 1 and the direction of gravity are perpendicular to each other.As seen from the front in Fig. 4, gravity acts from top to bottom, and gear 6 rotates counterclockwise. Therefore, if the centrifugal force immediately before the engine stops becomes sufficiently small,
Immediately before the tappet 3 is pushed up, it returns to a predetermined position with a pressure reducing function.

Further, in each of the above embodiments, the gear is provided with a pin and the movable member is provided with a guide groove, but conversely, the gear may be provided with a guide groove and the movable member may be provided with a pin.

(Effects of the invention) As can be seen from the above explanation, the automatic pressure reducing device for a four-cycle engine according to the invention has only one movable member that acts centrifugally due to the rotation of the camshaft. The structure is extremely simple and the assembly is easy.

In addition, there is only one movable member involved in the automatic pressure reduction operation, and the tappet is pushed up directly without any interference, so the pressure reduction operation is accurate, the starting load is smoothly reduced, and the operability when starting the engine is significantly improved. It has the effect of

By selecting the shape of the movable member and appropriately setting the position of the center of gravity, the same effect can be obtained even when the return spring is removed.

[Brief explanation of the drawing]

Fig. 1 is a front view showing an embodiment of the automatic pressure reduction device for a four-cycle engine according to the present invention, Fig. 2 is a sectional view taken along the line A-A in Fig. 1, and Fig. 3 is the automatic pressure reduction device in Fig. 1. FIG. 4 is a front view showing another embodiment of the automatic pressure reducing device for a four-cycle engine according to the present invention, and FIG.
Fig. 6 is a front view showing the state of the automatic pressure reducing device in normal operation, Fig. 6 is an explanatory diagram of the operation of the embodiment of the present invention shown in Fig. 1, and Fig. 7 is a front view of the automatic pressure reducing device of the conventional 4-cycle engine. It is a front view showing a representative example. 1... Camshaft, 2... Cam, 2a... Cam base circle, 3... Tappet, 4... Combustion chamber,
5... Intake valve or exhaust valve, 6... Gear, 20...
Movable member, 21... Oval guide groove, 22...
L-shaped guide groove, 23, 24...pin, 25...
Tappet push-up arm, 26... hole, 27... spring, 28... movable member, 29... through hole, 29a
... Narrow part of the through hole, 30 ... L-shaped guide groove, 3
1... L-shaped notch guide groove, 32, 33... Pin, 34... Valve spring.

Claims (1)

[Scope of utility model registration request] In a 4-stroke engine, a cam on the camshaft reciprocates a tappet as the camshaft rotates to open and close the intake and exhaust valves of the combustion chamber. A member is arranged and engaged with the gear so as to slide in a direction regulated by two guide grooves provided on the movable member and two pins provided on the side of the gear. The tappet pushing arm that pushes up the tappet during the stroke is extended, and the centrifugal force that acts on the movable member during engine startup rotation is caused by the gravity that opposes the centrifugal force, the frictional force between the guide groove and the pin, and the gear and The tappet push-up arm is made to protrude outside the cam base circle without exceeding the acting force of a return spring tensioned on the movable member, and the movable member acts on the tappet push-up arm via the tappet. The return force of the member is supported by the guide groove and the pin, and the centrifugal force acting on the movable member during normal rotation exceeds the opposing gravity, the frictional force, and the acting force of the return spring, so that the movable member is An automatic pressure reducing device for a four-stroke engine, characterized in that the tappet pushing-up arm slides along the guide so that it is located at the same position as the cam base circle or inside the cam base circle.